You are looking at the HTML representation of the XML format.
HTML is good for debugging, but is unsuitable for application use.
Specify the format parameter to change the output format.
To see the non HTML representation of the XML format, set format=xml.
See the complete documentation, or API help for more information. 
<?xml version="1.0"?>
<api>
  <query-continue>
    <allfileusages gafcontinue="Env1.png" />
  </query-continue>
  <query>
    <pages>
      <page pageid="172" ns="6" title="File:BST example.png" />
      <page pageid="173" ns="6" title="File:Balanced vs unbalanced BST.png" />
      <page pageid="169" ns="6" title="File:Binary tree.png" />
      <page pageid="243" ns="6" title="File:Cars.jpg" />
      <page pageid="945" ns="6" title="File:Casinovietqq188 song bai truc tuyen casino online uy tin hang dau Viet Nam.jpg" />
      <page pageid="140" ns="6" title="File:Compound statement.png" />
      <page pageid="275" ns="6" title="File:Cs61a.png" />
      <page pageid="174" ns="6" title="File:Decision tree.png" />
      <page pageid="257" ns="6" title="File:Deep list.png" />
      <page pageid="272" ns="6" title="File:Down Arrow Icon.png" />
    </pages>
  </query>
</api>